1. Field of the Invention
This invention relates to a camera being capable of simultaneously imaging scenes respectively seen in a plurality of directions and to an apparatus for visual recognition of surroundings of a vehicle, which uses such a camera.
2. Description of the Related Art
FIG. 11 is a diagram illustrating an operation of a vehicle equipped with a conventional apparatus for visual recognition of surroundings of a vehicle.
Generally, when a motor vehicle 15 is about to come in an intersection, a region indicated by oblique lines in FIG. 11 becomes a driver's blind spot 17. Further, the driver cannot visually recognize other motor vehicles 16 that are present in the left-side and right-side blind spots 17, respectively, as viewed in this figure.
Thus, to enable the driver to visually recognize the condition of the dead spot, there has been put to actual or practical use an apparatus for visual recognition of surroundings of the motor vehicle, in which a camera 18 is mounted on the front cover thereof and images of the left-side and right-side blind spots are simultaneously taken by the aforesaid camera 18 and thus the images of the blind spots are displayed on the screen of a monitor television 8 as shown in FIG. 12.
Next, an example of the conventional camera will be described hereinbelow with reference to FIG. 13.
Outer casing 4 serving as a housing is provided with entrance windows 4a and 4b in the left and right side portions thereof, respectively, so that extraneous light coming from the right and left can be incident thereon. Further, an image formation lens 3 is mounted in the outer casing 4. Image pickup device 13 constituted by CCD is placed at a focal point of the image formation lens 3. Moreover, a pair of first mirrors 10a and 10b are disposed at the left and right sides of the image formation lens 3, respectively. Furthermore, a pair of second mirrors 11a and 11b are placed in such a manner as to face the first mirrors 10a and 10b, respectively.
In the case of a camera 18A configured in this manner, extraneous light 5a coming from the right (namely, from above as viewed in FIG. 13) is incident on the outer casing 4 through the entrance window 4a. First, the extraneous light 5a is reflected by the first mirror 10a. Subsequently, the extraneous light 5a is further reflected by the second mirror 11a. Then, the extraneous light 5a reflected by this second mirror 11a is led to the image formation lens 3, so that an inverted (or vertically-flipped) normal image is formed on the left-side half of an imaging plane (namely, an image pickup plane) of the image pickup device 13.
On the other hand, the extraneous light 5b coming from the left (namely, from below as viewed in FIG. 13) is incident on the outer casing 4 through the entrance window 4b. Then, the extraneous light 5b is first reflected by a first mirror 10b. Subsequently, the extraneous light 5b is further reflected by the second mirror 11b. The extraneous light 5b reflected by this second mirror 11b is led to the image formation lens 3, so that an inverted normal image is formed on a right half of the imaging plane of the image pickup device 13.
Thus, this camera 18A is applied to an apparatus for visual recognition of surroundings of a vehicle, a picture signal representing an inverted normal image, which is formed from light received by the image pickup device 13, is displayed on the screen of the monitor television so that a scene, whose image is taken, is displayed in such a way as to be upside down. Thus, as illustrated in FIG. 12, a normal image formed from the extraneous light 5a coming from the right is displayed on the right-hand part of the screen of the monitor television 8. Further, another normal image formed from the extraneous light 5b coming from the left is displayed on the left-hand part of the screen of the monitor television 8. Thus, the driver can check the conditions of the left and right blind spots from the screen of the monitor television.
In the case of this camera 18A, a normal image is obtained by reflecting the extraneous light 5a (or 5b) two times by means of the first and second mirrors 10a and 11a (or 10b and 11b), namely, by changing an image, which is obtained as a mirror image by the first mirror 10a (or 10b), into the normal image by the use of the second mirror 11a (or 11b).
Here, note that when using only the first mirror 10a (or 10b) without using the second mirror 11a (or 11b), an image formed from light, which is received by the image pickup device 1, is an inverted mirror image. In this case, a mirror image CCD, which is operative to output a received light signal by horizontally flipping an image represented by the signal, is used as the image pickup device 13. Further, an inverted mirror image, which is represented by a picture signal obtained from the received light, is flipped from side to side, so that a picture signal representing an inverted normal image is outputted from the image pickup device 13. Moreover, this picture signal is displayed on the screen of the monitor television in such a manner that the image is upside down. Thus, as shown in FIG. 14, a normal image obtained from the extraneous light 5b coming from the left is unwillingly displayed on the right-hand half 8a of the screen of the monitor television 8. Furthermore, a normal image obtained from the extraneous light 5a coming from the right is unwillingly displayed on the left-hand half 8b of the screen of the monitor television 8. As a result, the direction, in which an image is displayed on the screen of the monitor television, is opposite to the direction of incidence of the light representing the image. Consequently, the images displayed on the screen of the monitor television is difficult for the driver to observe.
Next, another example of a conventional camera will be described hereinbelow with reference to FIG. 15.
This conventional camera 18B has a similar structure as of the aforementioned camera 18A except that prisms are used instead of reflection mirrors and that a mirror CCD is used as the image pickup device 13. Namely, a pair of prisms 6a and 6b are placed in a stage prior to the image formation lens 3 in such a way as to be on the upper and lower sides of the central axis and be parallel with each other.
In the case of the camera 18B configured in this way, the extraneous light 5a coming from the right (namely, from the right as viewed in FIG. 15) is incident on the outer casing 4 through the entrance widow 4a, and then is incident on the prism 6a and subsequently, is reflected by a reflection surface 7a and is then led to the image formation lens 3. Finally, an inverted mirror image is formed on the lower half of the imaging plane of the image pickup device 13.
On the other hand, the extraneous light 5b coming from the left (namely, from the left as viewed in FIG. 15) is incident on the outer casing 4 through the entrance window 4b, and is then incident on the prism 6b, and is subsequently reflected by the reflection surface 7b and is then led to the image formation lens 3. Finally, an inverted mirror image is formed on the upper half of the imaging plane of the image pickup device 13.
In the case this camera 18B, the reflection is performed once, so that the miniaturization of the camera can be achieved. However, an image formed in the image pickup device 13 is unwillingly a mirror image.
Thus, in the case that this camera 18B is applied to an apparatus for visual recognition of surroundings of a vehicle, a picture signal representing an inverted normal image, which is formed from light received by the image pickup device 13 in such a manner as to be flipped from side to side, is displayed on the screen of the monitor television so that a scene, whose image is taken, is displayed in such a way as to be upside down. Thus, as illustrated in FIG. 16, a normal image formed from the extraneous light 5a coming from the right is displayed on the upper half 9a of the screen of the monitor television 8. Further, another normal image formed from the extraneous light 5b coming from the left is displayed on the lower half 9b of the screen of the monitor television 8. Thereby, the driver can check the conditions of the left and right blind spots from the screen of the monitor television.
In the case of the conventional camera 18A using reflection mirrors, the incident light is reflected twice by the first and second mirrors. Therefore, this conventional camera has a problem that the size thereof is large.
On the other hand, in the case of the conventional camera 18B using two prisms, a normal image formed from the extraneous light 5a coming from the right is displayed on the upper screen of the monitor television, while a normal image formed from the extraneous light 5b coming from the left is displayed on the lower screen of the monitor television. This camera 18B, therefore, has problems that when applying this camera 18B to the apparatus for visual recognition of surroundings of a vehicle, the image displayed on the screen of the monitor television is difficult for the driver to observe, and that this camera 18B requires a plurality of prisms and thus a reduction in the cost thereof cannot be achieved.